Information storage devices are used to retrieve and/or store data in computers and other consumer electronics devices. A magnetic hard disk drive is an example of an information storage device that includes one or more heads that can both read and write, but other information storage devices also include heads—sometimes including heads that cannot write. A head that can read may be referred to as a “read head” herein, even if it includes other structures and functions such as a transducer for writing, a heater, microactuator, electronic lapping guide, laser diode, etc.
In a modern magnetic hard disk drive device, each head is a sub-component of a head gimbal assembly (HGA) that typically includes a suspension assembly with a laminated flexure to carry the electrical signals to and from the head. The HGA, in turn, is a sub-component of a head stack assembly (HSA) that typically includes a plurality of HGAs, an actuator, and a flexible printed circuit. The plurality of HGAs are attached to various arms of the actuator.
Contemporary read heads typically include a read sensor (e.g. a tunneling magnetoresistive or so-called “giant” magnetoresistive read sensor) that is merged with an inductive write transducer to effect reading and writing from/to a recording media (e.g. disk or tape). Typically the read sensor includes a ferromagnetic “free layer” that has a magnetic orientation that changes relative to a ferromagnetic “pinned layer,” due to externally applied magnetic fields from the recording media. The magnetic orientation of the pinned layer is fixed or pinned, so that the changes in magnetic orientation of the free layer are effectively changes in the relative magnetic orientation of the free layer and pinned layer. Typically, the free layer is separated from the pinned layer by a non-magnetic metallic spacer layer in the case of giant magnetoresistive (GMR) heads. Typically, the free layer is separated from the pinned layer by an insulative and typically ceramic barrier layer in the case of tunneling magnetoresistive (TMR) heads.
Recently, due to an industrial need for read sensors having increased sensitivity, there has been increased interest in read sensors having dual (or more) free layers separated by a spacer layer or barrier layer. In such read sensors, the magnetic orientation of each free layer may be biased so that it rotates oppositely from that of the free layer on the other side of the spacer or barrier layer, in response to an externally applied magnetic field from the recording media. Such opposite rotation has been termed as a so-called “scissor” mode of operation.
However, the performance of such dual free layer read sensors (e.g. the magnetoresistive ratio) depends upon the coupling between the free layers, their composition, and their internal structure. Hence, there is a need in the art for improved free layer compositions and structures that may provide or improve a desired free layer coupling and/or otherwise enhance the performance of dual free layer read sensors.